Memory device and method of manufacturing the same

ABSTRACT

A method of manufacturing a memory device includes sequentially forming and then etching a preliminary selection device layer, a preliminary middle electrode layer, and a preliminary variable resistance layer on a substrate, thereby forming a selection device, a middle electrode, and a variable resistance layer. At least one of a side portion of the selection device or a side portion of the variable resistance layer is removed so that a first width of the middle electrode in a first direction parallel to a top of the substrate is greater than a second width of the variable resistance layer in the first direction or a third width of the selection device in the first direction. A capping layer is formed on at least one of a side wall of the etched side portion of the selection device or a side wall of the etched side portion of the variable resistance layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/342,497, filed on Nov. 3, 2016, which claims priority under 35 U.S.C.§119 to Korean Patent Application No. 10-2016-0020681, filed on Feb. 22,2016, in the Korean Intellectual Property Office, the disclosure ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

Exemplary embodiments of the present inventive concept relate to amemory device, and more particularly to a method of manufacturing thesame.

DISCUSSION OF RELATED ART

With the lightening, thinning, and miniaturizing trend of electronicproducts, the demand for high-integration of semiconductor devices hasincreased. Memory devices having a three-dimensional (3D) cross-pointstructure in which a memory cell is disposed at a cross point betweentwo electrodes have been proposed. When down-scaling of memory deviceshaving a cross-point structure, widths and/or thicknesses ofsubstantially all layers in each memory device may also be reduced.Thus, the electrical characteristic and reliability of the down-scaledmemory devices may be reduced.

SUMMARY

Exemplary embodiments of the present inventive concept provide a memorydevice having a cross-point array type, which may have excellentelectrical characteristics and increased reliability, and a method ofmanufacturing the same.

According to an exemplary embodiment of the present inventive concept, amethod of manufacturing a memory device includes sequentially forming apreliminary selection device layer, a preliminary middle electrodelayer, and a preliminary variable resistance layer on a substrate. Thepreliminary selection device layer, the preliminary middle electrodelayer, and the preliminary variable resistance layer are etched, therebyforming a selection device, a middle electrode, and a variableresistance layer sequentially stacked on the substrate. At least one ofa side portion of the selection device or a side portion of the variableresistance layer is removed so that a first width of the middleelectrode in a first direction parallel to a top of the substrate isgreater than a second width of the variable resistance layer in thefirst direction or a third width of the selection device in the firstdirection. A capping layer is formed on at least one of a side wall ofthe etched side portion of the selection device or a side wall of theetched side portion of the variable resistance layer.

According to an exemplary embodiment of the present inventive concept, amethod of manufacturing a memory device includes sequentially forming apreliminary selection device layer, a preliminary middle electrodelayer, and a preliminary variable resistance layer on a substrate. Thepreliminary selection device layer, the preliminary middle electrodelayer, and the preliminary variable resistance layer are etched, therebyforming a selection device, a middle electrode, and a variableresistance layer which are sequentially stacked on the substrate. Atleast one of a side portion of the selection device or a side portion ofthe variable resistance layer is removed so that a first width of themiddle electrode in a first direction parallel to a top of the substrateis greater than a second width of the variable resistance layer in thefirst direction or a third width of the selection device in the firstdirection. A capping layer is formed on at least one of a side wall ofthe etched side portion of the selection device and a side wall of theetched side portion of the variable resistance layer. An insulationpattern is formed on a side wall of the capping layer and a side wall ofthe middle electrode by using a material having a dielectric constantless than a dielectric constant of the capping layer.

According to an exemplary embodiment of the present inventive concept, amemory device includes a plurality of first word lines extending in afirst direction parallel to a top of a substrate. A plurality of bitlines extends in a second direction on the substrate, the seconddirection being different from the first direction. A plurality ofmemory units are respectively arranged at cross points between theplurality of bit lines and the plurality of first word lines, each ofthe plurality of memory units including a selection device, a middleelectrode, and a variable resistance layer. A first capping layer isdisposed on a side wall of a recessed portion of each of the variableresistance layers and a second capping layer is disposed on a side wallof a recessed portion of each of the selection devices. The secondcapping layer is spaced apart from the first capping layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the inventive concept will become moreapparent by describing in detail exemplary embodiments thereof, withreference to the accompanying drawing, in which:

FIG. 1 is an equivalent circuit diagram of a memory device according toan exemplary embodiment of the present inventive concept;

FIG. 2 is a perspective view illustrating a memory device according toan exemplary embodiment of the present inventive concept;

FIG. 3 is a cross-sectional view taken along line X1-X1′ and line Y1-Y1′of FIG. 2;

FIG. 4 is a cross-sectional view taken along line X2-X2′ and line Y2-Y2′of FIG. 2;

FIG. 5 is a graph schematically showing a voltage-current curve of anovonic threshold switching (OTS) device having OTS characteristic;

FIG. 6 is a cross-sectional view illustrating a memory device accordingto an exemplary embodiment of the present inventive concept;

FIG. 7 is a cross-sectional view illustrating a memory device accordingto an exemplary embodiment of the present inventive concept;

FIG. 8 is a cross-sectional view illustrating a memory device accordingto an exemplary embodiment of the present inventive concept;

FIG. 9 is a cross-sectional view illustrating a memory device accordingto an exemplary embodiment of the present inventive concept;

FIG. 10 is a perspective view illustrating a memory device according toan exemplary embodiment of the present inventive concept;

FIG. 11 is a cross-sectional view taken along line X1-X1′ and lineY1-Y1′ of FIG. 10;

FIG. 12 is an equivalent circuit diagram of a memory device according toan exemplary embodiment of the present inventive concept;

FIG. 13 is a perspective view illustrating a memory device according toan exemplary embodiment of the present inventive concept;

FIG. 14 is a cross-sectional view taken along line X1-X1 of FIG. 13;

FIGS. 15A to 15O are cross-sectional views illustrating a method ofmanufacturing a memory device according to an exemplary embodiment ofthe present inventive concept;

FIGS. 16A to 16G are cross-sectional views illustrating a method ofmanufacturing a memory device according to an exemplary embodiment ofthe present inventive concept;

FIGS. 17A to 17D are cross-sectional views illustrating a method ofmanufacturing a memory device according to an exemplary embodiment ofthe present inventive concept;

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is an equivalent circuit diagram of a memory device according toan exemplary embodiment of the present inventive concept.

Referring to FIG. 1, a memory device 100 may include a plurality of wordlines WL1 to WL4 that extend along a first direction and are spacedapart from each other in a second direction perpendicular to the firstdirection. The memory device 100 may include a plurality of bit linesBL1 to BL4 that extend along the second direction and are spaced apartfrom each other in the first direction. The memory device 100 mayinclude a memory unit MC positioned at each cross point between the wordlines WL1 to WL4 and the bit lines BL1 to BL4.

The memory unit MC may include a variable resistance layer ME forstoring information and a selection device SW for selecting the memoryunit MC. In the memory unit MC positioned between the word line WL1 andthe bit line BL1, the variable resistance layer ME may be electricallyconnected to the word line WL1, the selection device SW may beelectrically connected to the bit line BL1, and the variable resistancelayer ME and the selection device SW may be serially connected to eachother. However, exemplary embodiments of the present inventive conceptare not limited thereto. For example, in an exemplary embodiment of thepresent inventive concept, in the memory unit MC, the selection deviceSW may be directly connected to the word line WL1, and the variableresistance layer ME may be directly connected to the bit line BL1.

A voltage may be applied to the variable resistance layer ME of thememory unit MC through the word lines WL1 to WL4 and the bit lines BL1to BL4, and thus, a current may flow in the variable resistance layerME. The variable resistance layer ME may include a phase change materiallayer which reversibly shifts between a first state and a second state.However, the variable resistance layer ME is not limited thereto. Forexample, in an exemplary embodiment of the present inventive concept,the variable resistance layer ME may include an arbitrary variableresistor whose resistance value varies according to a voltage appliedthereto. For example, a resistance of the variable resistance layer MEmay be reversibly shifted between the first state and the second stateaccording to a voltage applied to the variable resistance layer ME of aselected memory unit MC.

The memory unit MC may store digital information such as “0” or “1” inaccordance with a resistance change of the variable resistance layer ME,and the digital information may be erased from the memory unit MC. Forexample, data may be written as a high resistance state “0” and a lowresistance state “1” in the memory unit MC. Writing from the highresistance state “0” to the low resistance state “1” may be referred toas a set operation, and writing from the low resistance state “1” to thehigh resistance state “0” may be referred to as a reset operation.However, the memory unit MC according to exemplary embodiments of thepresent inventive concept is not limited to only digital informationcorresponding to the high resistance state “0” and the low resistancestate “1” and may store various resistance states.

An arbitrary memory unit MC may be addressed by selecting the word linesWL1 to WL4 and the bit lines BL1 to BL4 and may be programmed byapplying a certain signal between the word lines WL1 to WL4 and the bitlines BL1 to BL4, and information based on a resistance value of avariable resistor configuring the arbitrary memory unit MC may be readout by measuring a current value through the bit lines BL1 to BL4.

In the memory device 100 according to an exemplary embodiment of thepresent inventive concept, a plurality of capping layers 142 and 144(see, e.g., FIG. 2) may be respectively formed on a side wall of thevariable resistance layer ME and a side wall of the selection device SW.For example, referring to FIG. 2, a plurality of capping layer 142 maybe formed on sidewalls of a variable resistance layer 132, and aplurality of capping layers 144 may be formed on sidewalls of aselection device 134. A plurality of insulation patterns 150 and 160(see, e.g., FIG. 2) including a material having a dielectric constantlower than those of the capping layers 142 and 144 may be formed in aspace between adjacent memory units MC. For example, referring to FIG.2, the plurality of insulation patterns 150 and 160 may be formedbetween each of a plurality of memory cell pillars 130. Thus, RC delaycaused by a reduction in dimension of the memory device 100 may bereduced or eliminated, and thus, the memory device 100 may operate at arelatively high speed.

FIG. 2 is a perspective view illustrating the memory device according toan exemplary embodiment of the present inventive concept. FIG. 3 is across-sectional view taken along line X1-X1′ and line Y1-Y1′ of FIG. 2.FIG. 4 is a cross-sectional view taken along line X2-X2′ and line Y2-Y2′of FIG. 2.

Referring to FIGS. 2 to 4, the memory device 100 may include a pluralityof word lines 110, which extend in a first direction (e.g., an Xdirection) on a substrate 102, and a plurality of bit lines 120 whichextend in a second direction (e.g., a Y direction) perpendicular to thefirst direction.

An insulating interlayer 105 may be disposed on the substrate 102. Theinsulating interlayer 105 may include an oxide, such as silicon oxide,or a nitride such as silicon nitride. The insulating interlayer 105 mayelectrically separate the plurality of word lines 110 from the substrate102.

The plurality of word lines 110 and the plurality of bit lines 120 mayeach include metal, conductive metal nitride, conductive metal oxide, ora combination thereof. In an exemplary embodiment of the presentinventive concept, the plurality of word lines 110 and the plurality ofbit lines 120 may each include tungsten (W), tungsten nitride (WN), gold(Au), silver (Ag), copper (Cu), aluminium (Al), titanium aluminiumnitride (TiAlN), iridium (Ir), platinum (Pt), palladium (Pd), ruthenium(Ru), zirconium (Zr), rhodium (Rh), nickel (Ni), cobalt (Co), chromium(Cr), tin (Sn), zinc (Zn), indium tin oxide (ITO), an alloy thereof, ora combination thereof. In an exemplary embodiment of the presentinventive concept, the plurality of word lines 110 and the plurality ofbit lines 120 may each include a metal layer and a conductive barrierlayer covering at least a portion of the metal layer. The conductivebarrier layer may include, for example, titanium (Ti), TiN, tantalum(Ta), TaN, or a combination thereof.

Referring to FIGS. 2 to 4, according to an exemplary embodiment of thepresent inventive concept, the plurality of word lines 110 may bedisposed on the substrate 102 and the plurality of bit lines 120 may bedisposed on the plurality of word lines 110, but exemplary embodimentsof the present inventive concept are not limited thereto. According toan exemplary embodiment of the present inventive concept, the pluralityof bit lines 120 may extend in the first direction or the seconddirection on the substrate 102, and the plurality of word lines 110 mayextend in the second direction or the first direction on the pluralityof bit lines 120.

Referring to FIG. 2, each of the word lines 110 extending in the firstdirection (e.g., the X direction) may cross each of the bit lines 120extending in the second direction (e.g., the Y direction). A pluralityof memory units MC may be respectively disposed at a plurality of crosspoints between the plurality of word lines 110 and the plurality of bitlines 120.

Each of the plurality of memory units MC may include a memory cellpillar 130. Each of the memory cell pillars may include a top electrodeTE, the variable resistance layer 132, a middle electrode ME, theselection device 134, and a bottom electrode BE.

In an exemplary embodiment of the present inventive concept, thevariable resistance layer 132 may include a phase change material whichreversibly changes between a crystalline state and an amorphous stateaccording to a heating duration. For example, the variable resistancelayer 132 may include a material of which phase reversibly changes dueto Joule heat generated by a voltage applied between both ends of thevariable resistance layer 132. A resistance of the material may changewith the phase change. The phase change material may be in a highresistance state in an amorphous phase and may be in a low resistancestate in a crystalline phase. The high resistance state may be definedas 0, and the low resistance state may be defined as 1, and thus datamay be stored in the variable resistance layer 132.

In an exemplary embodiment of the present inventive concept, thevariable resistance layer 132 may include one or more elements (e.g., achalcogen element) from periodic table Group VI and may additionallyinclude one or more chemical modifiers from Group III, IV or V. Forexample, the variable resistance layer 132 may include Ge—Sb—Te. Achemical composition mark including hyphens (-) may represent a certaincompound or an element included in a compound and may represent allchemical formula structures including a represented element. Forexample, Ge—Sb—Te may be a material such as Ge₂Sb₂Te₅, Ge₂Sb₂Te₇,Ge₁Sb₂Te₄, Ge₁Sb₄Te₇, or the like.

The variable resistance layer 132 may include various phase changematerials in addition to Ge—Sb—Te. For example, the variable resistancelayer 132 may include at least one of Ge—Te, Sb—Te, In—Se, Ga—Sb, In—Sb,As—Te, Al—Te, Bi—Sb—Te (BST), In—Sb—Te (IST), Ge—Sb—Te, Te—Ge—As,Te—Sn—Se, Ge—Se—Ga, Bi—Se—Sb, Ga—Se—Te, Sn—Sb—Te, In—Sb—Ge, In—Ge—Te,Ge—Sn—Te, Ge—Bi—Te, Ge—Te—Se, As—Sb—Te, Sn—Sb—Bi, Ge—Te—O, Te—Ge—Sb—S,Te—Ge—Sn—O, Te—Ge—Sn—Au, Pd—Te—Ge—Sn, In—Se—Ti—Co, Ge—Sb—Te—Pd,Ge—Sb—Te—Co, Sb—Te—Bi—Se, Ag—In—Sb—Te, Ge—Sb—Se—Te, Ge—Sn—Sb—Te,Ge—Te—Sn—Ni, Ge—Te—Sn—Pd, Ge—Te—Sn—Pt, In—Sn—Sb—Te, or As—Ge—Sb—Te or acombination thereof.

Each of elements included in the variable resistance layer 132 may havevarious stoichiometry ratios. A crystallization temperature, a meltingtemperature, a phase change speed based on crystallization energy, anddata retention characteristic of the variable resistance layer 132 maybe adjusted based on the stoichiometry ratio of each element.

The variable resistance layer 132 may include at least one impurity,such as, carbon (C), nitrogen (N), silicon (Si), oxygen (O), bismuth(Bi), or tin (Sn). A driving current of the memory device 100 may bechanged by the at least one impurity. The variable resistance layer 132may include at least one metal. For example, the variable resistancelayer 132 may include at least one of aluminium (Al), gallium (Ga), tin(Sn), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt(Co), nickel (Ni), molybdenum (Mo), ruthenium (Ru), palladium (Pd),hafnium (Hf), tantalum (Ta), iridium (Ir), platinum (Pt), zirconium(Zr), thallium (Tl), lead (Pb), titanium (Ti), or polonium (Po). Themetal may increase the electrical conductivity and thermal conductivityof the variable resistance layer 132 and may thus increase acrystallization speed, thus increasing a set speed. The metal mayincrease the data retention characteristics of the variable resistancelayer 132.

The variable resistance layer 132 may have a multilayer structure inwhich two or more layers having different physical properties arestacked. The number or thickness of the layers may be selected, asdesired. A barrier layer may be formed between the layers. The barrierlayer may prevent materials from being diffused between the layers. Asan example, the barrier layer may decrease diffusion of a precedinglayer when forming a subsequent layer among the layers.

The variable resistance layer 132 may have a super-lattice structure inwhich a plurality of layers including different materials arealternately stacked. For example, the variable resistance layer 132 mayinclude a structure where a first layer including Ge—Te and a secondlayer including Sb—Te are alternately stacked. However, exemplaryembodiments of the present inventive concept are not limited thereto,and a material of the first layer is not limited to Ge—Te, and amaterial of the second layer is not limited to Sb—Te. The first andsecond layers may each include the above-described various materials.

The variable resistance layer 132 has been described above as includinga phase change material. However, exemplary embodiments of the presentinventive concept are not limited thereto. For example, in an exemplaryembodiment of the present inventive concept, the variable resistancelayer 132 of the memory device 100 may include various materials havingresistance-changing characteristic.

In some exemplary embodiments of the present inventive concept, when thevariable resistance layer 132 includes transition metal oxide, thememory device 100 may be a resistive random access memory (ReRAM). Inthe variable resistance layer 132 including transition metal oxide, atleast one electrical path may be formed or depleted in the variableresistance layer 132 through a program operation. When the electricalpath is formed, the variable resistance layer 132 may have a lowresistance value, and when the electrical path is depleted, the variableresistance layer 132 may have a high resistance value. The memory device100 may store data by using a resistance value difference of thevariable resistance layer 132.

When the variable resistance layer 132 includes transition metal oxide,the transition metal oxide may include at least one metal, such as, Ta,Zr, Ti, Hf, Mn, Y, Ni, Co, Zn, Nb, Cu, Fe, or Cr. For example, thetransition metal oxide may have a single layer or a multilayer structureincluding at least one material selected from among Ta₂O_(5-x),ZrO_(2-x), TiO_(2-x), HfO_(2-x), MnO_(2-x), Y₂O_(3-x), NiO_(1-y),Nb₂O_(5-x), CuO_(1-y), or Fe₂O_(3-x). In the above-described materials,x may be selected within a range of 0≦x≦1.5, and y may be selectedwithin a range of 0≦y≦0.5. However, exemplary embodiments of the presentinventive concept are not limited thereto.

In an exemplary embodiment of the present inventive concept, when thevariable resistance layer 132 has a magnetic tunnel junction (MJT)structure which includes two electrodes including a magnetic materialand a dielectric disposed between the two magnetic electrodes, thememory device 100 may be a magnetic random access random (MRAM).

The two electrodes may respectively be a magnetization fixed layer and amagnetization free layer, and the dielectric disposed therebetween maybe a tunnel barrier layer. The magnetization fixed layer may have amagnetization direction which is fixed in one direction, and themagnetization free layer may have a magnetization direction which ischangeable to be parallel or antiparallel to the magnetization directionof the magnetization fixed layer. The magnetization directions of themagnetization fixed layer and the magnetization free layer may beparallel to one surface of the tunnel barrier layer, but exemplaryembodiments of the present inventive concept are not limited thereto. Inan exemplary embodiment of the present inventive concept, themagnetization directions of the magnetization fixed layer and themagnetization free layer may be perpendicular to the one surface of thetunnel barrier layer.

When the magnetization direction of the magnetization free layer isparallel to the magnetization direction of the magnetization fixedlayer, the variable resistance layer 132 may have a first resistancevalue. When the magnetization direction of the magnetization free layeris antiparallel to the magnetization direction of the magnetizationfixed layer, the variable resistance layer 132 may have a secondresistance value. By using such a resistance value difference, thememory device 100 may store data. The magnetization direction of themagnetization free layer may be changed by a spin torque of electronsincluded in a program current.

The magnetization fixed layer and the magnetization free layer may eachinclude a magnetic material. In this case, the magnetization fixed layermay further include an antiferromagnetic material that fixes amagnetization direction of a ferromagnetic material included in themagnetization fixed layer. The tunnel barrier layer may include at leastone oxide, such as, Mg, Ti, Al, MgZn, or MgB, but exemplary embodimentsof the present inventive concept are not limited thereto.

The selection device 134 may be a current control element forcontrolling a flow of a current. The selection device 134 may be, forexample, a current control element having ovonic threshold switching(OTS) characteristic.

The selection device 134 may include a material having a resistancewhich varies according to a level of a voltage applied across both endsof the selection device 134, and for example, may include a materialhaving the OTS characteristic. For example, when a voltage lower than athreshold voltage V_(T) is applied to the selection device 134, theselection device 134 may be in the high resistance state, and when avoltage higher than the threshold voltage V_(T) is applied to theselection device 134, the selection device 134 may be in the lowresistance state and a current may start to flow. When the currentflowing through the selection device 134 becomes lower than a holdingcurrent, the selection device 134 may be changed to the high resistancestate. The OTS characteristic of the selection device 134 will bedescribed below in more detail with reference to FIG. 5.

The selection device 134 may include a chalcogenide material as an OTSmaterial layer. A representative example of the chalcogenide materialmay include one or more elements (e.g., an chalcogen element) fromperiodic table Group VI and may additionally include one or morechemical modifiers from Group III, IV or V. Exemplary chalcogen elementscapable of being included in the selection device 134 may include sulfur(S), selenium (Se), or tellurium (Te). The chalcogen elements arecharacterized by including a divalent bonding and a lone pair electron.The divalent bonding leads to forming of a chain and ring structure bybonding chalcogen elements for forming a chalcogenide material, and thelone pair electron provides an electron source for forming a conductivefilament. For example, trivalent and tetravalent modifiers such as Al,Ga, indium (In), germanium (Ge), Sn, Si, phosphorus (P), arsenic (As),or antimony (Sb) may be added into a chain and ring structure of achalcogen element to determine a structural rigidity of a chalcogenidematerial and may classify the chalcogenide material into a switchingmaterial and a phase change material, based on a capability to performcrystallization or other structural rearrangement.

In some exemplary embodiments of the present inventive concept, theselection device 134 may include Si, Te, As, Ge, In, or a combinationthereof. For example, the selection device 134 may include about 14% Si,about 39% Te, about 37% As, about 9% Ge, and about 1% In. A percentageratio denotes an atomic percentage ratio where an atomic element is atotal of 100%.

The selection device 134 may include Si, Te, As, Ge, S, Se, or acombination thereof. For example, the selection device 134 may includeabout 5% Si, about 34% Te, about 28% As, about 11% Ge, about 21% S, andabout 1% Se.

The selection device 134 may include Si, Te, As, Ge, S, Se, Sb, or acombination thereof. For example, the selection device 134 may includeabout 21% Te, about 10% As, about 15% Ge, about 2% S, about 50% Se, andabout 2% Sb.

In the memory device 100 according to an exemplary embodiment of thepresent inventive concept, the selection device 134 is not limited tothe OTS material layer. For example, the selection device 134 mayinclude various material layers having a function of selecting deviceswithout being limited to the OTS material layer. For example, theselection device 134 may include a diode, tunnel junction, a PNP diodeor a bipolar junction transistor (BJT), or may employ mixedionic-electronic conduction (MIEC).

The bottom electrode BE may be disposed between the plurality of wordlines 110 and the selection device 134. The middle electrode ME may bedisposed between the selection device 134 and the variable resistancelayer 132. The top electrode TE may be disposed between the variableresistance layer 132 and the plurality of bit lines 120.

In an exemplary embodiment of the present inventive concept, the bottomelectrode BE, the middle electrode ME, and the top electrode TE may eachinclude metal, conductive metal nitride, conductive metal oxide, or acombination thereof. At least one of the bottom electrode BE, the middleelectrode ME, and the top electrode TE may include a conductive layer,including metal or conductive metal nitride, and at least one conductivebarrier layer covering at least a portion of the conductive layer. Theconductive barrier layer may include a metal oxide, metal nitride, or acombination thereof, but exemplary embodiments of the present inventiveconcept are not limited thereto.

In an exemplary embodiment of the present inventive concept, the topelectrode TE or the middle electrode ME contacting the variableresistance layer 132 may include a conductive material that generatesheat sufficient to phase-change the variable resistance layer 132. Forexample, the top electrode TE or the middle electrode ME may include arefractory metal such as TiN, TiSiN, TiAlN, TaSiN, TaAlN, TaN, WSi, WN,TiW, MoN, NbN, TiBN, ZrSiN, WSiN, WBN, ZrAlN, MoAIN, TiAl, TiON, TiAlON,WON, TaON, C, SiC, SiCN, CN, TiCN, TaCN, or a combination thereof, anitride thereof, or a carbon-based conductive material.

In an exemplary embodiment of the present inventive concept, a heaterelectrode may be disposed between the variable resistance layer 132 andthe top electrode TE or between the variable resistance layer 132 andthe middle electrode ME. The heater electrode may include a conductivematerial that generates heat sufficient to phase-change the variableresistance layer 132. For example, the heater electrode may include arefractory metal such as TiN, TiSiN, TiAlN, TaSiN, TaAlN, TaN, WSi, WN,TiW, MoN, NbN, TiBN, ZrSiN, WSiN, WBN, ZrAlN, MoAlN, TiAl, TiON, TiAlON,WON, TaON, C, SiC, SiCN, CN, TiCN, TaCN, or a combination thereof, anitride thereof, or a carbon-based conductive material.

Referring to FIGS. 2 to 4, the variable resistance layer 132 may bedisposed above the selection device 134 with the middle electrode MEdisposed between the selection device 134 and the variable resistancelayer 132, but exemplary embodiments of the present inventive conceptare not limited thereto. According to an exemplary embodiment of thepresent inventive concept, the selection device 134 may be disposedabove the variable resistance layer 132 with the middle electrode MEdisposed between the variable resistance layer 132 and the selectiondevice 134. The bottom electrode BE or the middle electrode MEcontacting the variable resistance layer 132 may include a conductivematerial that generates heat sufficient to phase-change the variableresistance layer 132. The heater electrode may be disposed between thevariable resistance layer 132 and the bottom electrode BE or between thevariable resistance layer 132 and the middle electrode ME.

A plurality of capping layers 142 and 144 may be respectively formed onside walls of the plurality of memory cell pillars 130. A first cappinglayer 142 may be disposed on a side wall of the variable resistancelayer 132, and a second capping layer 144 may be disposed on a side wallof the selection device 134.

In an exemplary embodiment of the present inventive concept, the firstcapping layer 142 may surround the side wall of the variable resistancelayer 132 and may contact a bottom of the top electrode TE and a top ofthe middle electrode ME. Referring to FIG. 2, the first capping layer142 may surround substantially the entire portion of the side wall ofthe variable resistance layer 132, but exemplary embodiments of thepresent inventive concept are not limited thereto.

The first capping layer 142 may include a pair of first portions 142X,which are disposed on the side wall of the variable resistance layer 132and are spaced apart from each other along the second direction (e.g.,the Y direction), and a pair of second portions 142Y which are disposedon the side wall of the variable resistance layer 132 and are spacedapart from each other along the first direction (e.g., the X direction).The pair of second portions 142Y may contact ends of the pair of firstportions 142X, and the pair of first portions 142X and the pair ofsecond portions 142Y may surround the side wall of the variableresistance layer 132.

Referring to FIG. 3, the pair of first portions 142X included in thefirst capping layer 142 may each include an outer wall 142X-OS and aninner wall 142X-IS which extend in the first direction (e.g., the Xdirection). The inner wall 142X-IS of the first capping layer 142 maycontact the side wall of the variable resistance layer 132. In anexemplary embodiment of the present inventive concept, the inner wall142X-IS of the first capping layer 142 may be substantially planar alonga third direction (e.g., a Z direction) As an example, the inner wall142X-IS of the first capping layer 142 may be vertically planar. Theouter wall 142X-OS of the first capping layer 142 may be aligned with aside wall of the middle electrode ME. The outer wall 142X-OS of thefirst capping layer 142 may be aligned with the side wall of the middleelectrode ME. An extension plane of the outer wall 142X-OS of the firstcapping layer 142 may be disposed on substantially a same plane as anextension plane of the side wall of the middle electrode ME.

Referring to FIG. 3, the pair of second portions 142Y included in thefirst capping layer 142 may each include an outer wall 142Y-OS and aninner wall 142Y-IS which extend in the second direction (e.g., the Ydirection). The inner wall 142Y-IS of the first capping layer 142contacting the side wall of the variable resistance layer 132 may besubstantially planar along the third direction (e.g., the Z direction).As an example, the inner wall 142Y-IS of the first capping layer 142contacting the side wall of the variable resistance layer 132 may bevertically planar. The outer wall 142Y-OS of the first capping layer 142may be aligned with the side wall of the middle electrode ME.

In an exemplary embodiment of the present inventive concept, the secondcapping layer 144 may surround the side wall of the selection device 134and may contact a bottom of the middle electrode ME and a top of thebottom electrode ME. Referring to FIG. 2, the second capping layer 144may surround substantially the entire portion of the side wall of theselection device 134, but exemplary embodiments of the present inventiveconcept are not limited thereto.

The second capping layer 144 may include at least two third portions144X, which are disposed on the side wall of the selection device 134and are spaced apart from each other along the second direction (e.g.,the Y direction), and at least two fourth portions 144Y which aredisposed on the side wall of the selection device 134 and are spacedapart from each other along the first direction (e.g., the X direction).The fourth portions 144Y may contact ends of the pair of third portions144X. The third portions 144X and the fourth portions 144Y may surroundthe side wall of the selection device 134.

Referring to FIG. 3, the pair of third portions 144X included in thesecond capping layer 144 may each include an outer wall 144X-OS and aninner wall 144X-IS which extend in the first direction (e.g., the Xdirection). The inner wall 144X-IS of the second capping layer 144 maycontact the side wall of the selection device 134. In an exemplaryembodiment of the present inventive concept, the inner wall 144X-IS ofthe second capping layer 144 may be substantially planar along the thirddirection (e.g., the Z direction). As an example, the inner wall 144X-ISof the second capping layer 144 may be vertically planar. The outer wall144X-OS of the second capping layer 144 may be aligned with the sidewall of the middle electrode ME.

The fourth portions 144Y included in the second capping layer 144 mayeach include an outer wall 144Y-OS and an inner wall 144Y-IS whichextend in the second direction (e.g., the Y direction). The inner wall144Y-IS of the second capping layer 144 contacting the side wall of theselection device 134 may be substantially planar along the thirddirection (e.g., the Z direction). The outer wall 144Y-OS of the secondcapping layer 144 may be aligned with the side wall of the middleelectrode ME.

In an exemplary embodiment of the present inventive concept, the firstcapping layer 142 and the second capping layer 144 may each includesilicon nitride or silicon oxynitride. However, a material of each ofthe first capping layer 142 and the second capping layer 144 is notlimited thereto. The first capping layer 142 and the second cappinglayer 144 may surround the side walls of the variable resistance layer132 and the selection device 134, respectively. The first capping layer142 and the second capping layer 144 may each act as a passivation layerthat prevents the variable resistance layer 132 and the selection device134 from being oxidized or damaged due to being exposed in a process ofmanufacturing the memory device 100, such as, in a process of etchingunderlying layers or a process of forming an insulation layer.

A plurality of first insulation patterns 150 may be respectivelydisposed between a plurality of memory cell pillars 130, arranged in arow along the second direction (e.g., the Y direction). A plurality ofsecond insulation patterns 160 may be respectively disposed between aplurality of memory cell pillars 130, arranged in one row along thefirst direction (e.g., the X direction).

Referring to FIGS. 2 to 4, the plurality of second insulation patterns160 may be line-type patterns which are spaced apart from each other inthe first direction and extend along the second direction. The pluralityof first insulation patterns 150 may be island-type patterns which arerespectively disposed between a plurality of memory cell pillars 130,between two adjacent second insulation patterns 160 among the pluralityof second insulation patterns 160. However, exemplary embodiments of thepresent inventive concept are not limited thereto According to anexemplary embodiment of the present inventive concept, the plurality offirst insulation patterns 150 may be line-type patterns which extendalong the second direction, and the plurality of second insulationpatterns 160 may be island-type patterns which are spaced apart fromeach other along the first direction and the second direction. Accordingto an exemplary embodiment of the present inventive concept, theplurality of first insulation patterns 150 may be island-type patternswhich are spaced apart from each other along the first direction and thesecond direction, and the plurality of second insulation patterns 160may be line-type patterns which extend along the first direction.

In an exemplary embodiment of the present inventive concept, theplurality of first insulation patterns 150 and the plurality of secondinsulation patterns 160 may each include a material which is lower indielectric constant than the capping layers 142 and 144. For example,the plurality of first insulation patterns 150 and the plurality ofsecond insulation patterns 160 may each include a silicon oxide, suchas, BPSG, PSG, USG, FSG, SOG, FOX, TEOS, PE-TEOS, HDP-CVD oxide, FSG, orSiOC.

Referring to FIG. 3, the middle electrode ME may have a first width W1in the second direction (e.g., the Y direction). A second width W2 ofthe variable resistance layer 132 in the second direction may be lessthan the first width W1 of the middle electrode ME. A third width W3 ofthe selection device 134 in the second direction may be less than thefirst width W1 of the middle electrode ME. The first width W1 of themiddle electrode ME may be from about 10 nm to about 200 nm, butexemplary embodiments of the present inventive concept are not limitedthereto. The second width W2 of the variable resistance layer 132 andthe third width W3 of the selection device 134 may be from about 5 nm toabout 180 nm, but exemplary embodiments of the present inventive conceptare not limited thereto. The first width W1 of the middle electrode ME,the second width W2 of the variable resistance layer 132, and the thirdwidth W3 of the selection device 134 and/or thicknesses of the middleelectrode ME, the variable resistance layer 132, and the selectiondevice 134 may be selected based on a degree of integration of thememory device 100, a resolution limitation of a photolithographyprocess, and a threshold voltage of the selection device 134.

In an exemplary embodiment of the present inventive concept, the firstcapping layer 142 may have a fourth width W4 in the second direction(e.g., the Y direction), and the second capping layer 144 may have afifth width W5 equal to the fourth width W4 in the second direction. Forexample, the fourth width W4 and the fifth width W5 may be from about 2nm to about 50 nm. However, exemplary embodiments of the presentinventive concept are not limited thereto. According to an exemplaryembodiment of the present inventive concept, the fourth width W4 of thefirst capping layer 142 may differ from the fifth width W5 of the secondcapping layer 144.

Generally, in a process of forming the plurality of memory cell pillars130 (for example, a process of etching the plurality of memory cellpillars 130, a process of etching the word lines 110 or the bit lines120, or a process of forming the plurality of insulation patterns 150and 160), when the variable resistance layer 132 including the phasematerial layer and the selection device 134 including the materialhaving the OTS characteristic are exposed to an atmosphere (e.g., air),damage such as being oxidized may occur in the variable resistance layer132 and the selection device 134. A passivation layer including siliconnitride may surround a side wall of each of the plurality of memory cellpillars 130, and thus damage, such as oxidation, may be reduced oreliminated. However, in a memory device including a cross-pointstructure, as a width of each of the memory cell pillars 130 is reduced,an interval between the memory cell pillars 130 may also be reduced. Inthis case, the passivation layer may fully fill the interval between thememory cell pillars 130. However, due to the passivation layer which hasa high dielectric constant generally, considerable RC delay may occur indriving the memory device.

However, in the memory device 100 according to an exemplary embodimentof the present inventive concept, the capping layers 142 and 144 havinga relatively thin thickness may be disposed on only the side walls ofthe variable resistance layer 132 and the selection device 134, and theplurality of insulation patterns 150 and 160 may be disposed between thememory cell pillars 130. The plurality of insulation patterns 150 and160 may include a material having a dielectric constant which is lowerthan that of each of the capping layers 142 and 144. Thus, RC delaywhich occurs in driving the memory device 100 may be reduced oreliminated, thus enabling the memory device 100 to operate at a highspeed.

In the memory device 100 according to an exemplary embodiment of thepresent inventive concept, since the capping layers 142 and 144 having arelatively thin thickness are disposed on only the side walls of thevariable resistance layers 132 and the selection devices 134, damage tothe variable resistance layers 132 and the selection devices 134 may bereduced or prevented in a process of manufacturing the memory device100. Thus, reliability of the memory device 100 may be increased.

In the memory device 100 according to an exemplary embodiment of thepresent inventive concept, the selection device 134 having the OTScharacteristic may be used. An OTS device may include a chalcogencompound which has an amorphous state in an on state and an off state.As an example, the OTS device may be repeatedly shifted between the offstate corresponding to a relatively low resistance and the on statecorresponding to a relatively high resistance by applying a voltage or acurrent without any change in phase of the chalcogen compound. Thus, theOTS device may have relatively high endurance (e.g., relatively highcycle characteristic and reliability). Even when a degree of integrationof the memory device 100 is relatively high, such as, when the memorydevice 100 is down-scaled, the selection device 134 in each of thememory cell pillars 130 may have a uniform threshold voltagedistribution. A switching operation of the OTS device will be describedin more detail below with reference to FIG. 5.

FIG. 5 is a graph schematically showing a voltage-current curve 60 of anOTS device having OTS characteristic. FIG. 5 schematically shows acurrent which flows in the OTS device according to a voltage appliedacross both ends of the OTS device having the OTS characteristic.

Referring to FIG. 5, a first curve 61 represents a voltage-currentrelationship in a state where a current does not flow in an OTS device.The OTS device may act as a switching device having a threshold voltageV_(T) which is at a first voltage level 63. When a voltage graduallyincreases from a state where the voltage and the current are 0, thecurrent hardly flows in the OTS device until the voltage reaches thethreshold voltage V_(T) (e.g., the first voltage level 63). However, assoon as the voltage exceeds the threshold voltage V_(T), the currentflowing in the OTS device may rapidly increase, and the voltage appliedto the OTS device may decrease to a second voltage level 64 (e.g., asaturation voltage V_(S)).

A second curve 62 represents a voltage-current relationship in a statewhere a current flows in the OTS device. As the current flowing in theOTS device has a level higher than a first current level 66, a voltageapplied to the OTS device may slightly further increase than the secondvoltage level 64. For example, while the current flowing in the OTSdevice is increasing from the first current level 66 to a second currentlevel 67, the voltage applied to the OTS device may slightly increasefrom the second voltage level 64. As an example, once the current flowsthrough the OTS device, the voltage applied to the OTS device may besubstantially maintained as the saturation voltage V_(S) e.g., thesecond voltage level 64). For example, when the current decreases toless than a holding current level (e.g., the first current level 66),the OTS device may be changed to a resistance state and may effectivelyblock the current until the voltage increases to the threshold voltageV_(T).

FIG. 6 is a cross-sectional view illustrating a memory device accordingto an exemplary embodiment of the present inventive concept. Referringto FIG. 6, like reference numerals may refer to like componentsdescribed with reference to FIGS. 1 to 5 and thus duplicativedescriptions may be omitted.

FIG. 6 illustrates a cross-sectional view corresponding to across-sectional view taken along line X1-X1′ of FIG. 2. Except for ashape of each of a first capping layer 142A and a second capping layer144A, a memory device 100 a described with reference to FIG. 6 may besubstantially the same as the memory device 100 described with referenceto FIGS. 2 to 4.

Referring to FIG. 6, a plurality of memory cell pillars 130A may eachinclude a variable resistance layer 132A, including a recessed portion132R disposed in a side wall of the variable resistance layer 132A, anda selection device 134A including a recessed portion 134R disposed in aside wall of the selection device 134A.

The side wall of the variable resistance layer 132A may include therecessed portion 132R recessed toward an inner side, and thus, a secondwidth W2 of the variable resistance layer 132A may gradually decrease ina direction from an upper side to a center portion and may graduallyincrease in a direction from the center portion to a lower side.Referring to FIG. 6, a tail may extend toward an outer side and may beformed in an uppermost side wall of the variable resistance layer 132A.A tail may be formed in a lowermost side wall of the variable resistancelayer 132A.

The side wall of the selection device 134A may include the recessedportion 134R recessed toward an inner side, and thus, a third width W3of the selection device 134A may gradually decrease in a direction froman upper side to a center portion and may gradually increase in adirection from the center portion to a lower side. Referring to FIG. 6,a tail may extend toward an outer side may be formed in an uppermostside wall of the selection device 134A. A tail may be formed in alowermost side wall of the selection device 134A. The first cappinglayer 142A may surround the recessed portion 132R of the variableresistance layer 132A. An outer wall 142A-OS of the first capping layer142A may be aligned with a side wall of a middle electrode ME and may besubstantially planar in a vertical direction (e.g., a Z direction).Alternatively, the outer wall 142A-OS of the first capping layer 142Amay be inclined at an angle with respect to the vertical direction. Aninner wall 142A-IS of the first capping layer 142A may be a rounded sidewall which contacts the recessed portion 132R of the variable resistancelayer 132A and protrudes in a direction toward the variable resistancelayer 132A.

The second capping layer 144A may surround the recessed portion 134R ofthe selection device 134A. An outer wall 144A-OS of the second cappinglayer 144A may be aligned with the side wall of the middle electrode MEand may be substantially planar in the vertical direction (e.g., the Zdirection). Alternatively, the outer wall 144A-OS of the second cappinglayer 144A may be inclined at an angle with respect to the verticaldirection. An inner wall 144A-IS of the second capping layer 144A may bea rounded side wall which contacts the recessed portion 134R of theselection device 134A and protrudes in a direction toward the selectiondevice 134A.

In an exemplary embodiment of the present inventive concept, therecessed portion 132R of the variable resistance layer 132A and therecessed portion 134R of the selection device 134A may be formed by anisotropic etching process for the variable resistance layer 132A and theselection device 134A. The first capping layer 142A and the secondcapping layer 144A may fill a portion of the variable resistance layer132A and a portion of the selection device 134A which are removed by theisotropic etching process, and thus, the first capping layer 142A andthe second capping layer 144A may respectively fill the rounded innerwall 142A-IS and the rounded inner wall 144A-IS.

Exemplary profiles of the recessed portion 132R of the variableresistance layer 132A and a profile of the recessed portion 134R of theselection device 134A are illustrated in FIG. 6. However, exemplaryembodiments of the present inventive concept are not limited thereto.The profile of the recessed portion 132R of the variable resistancelayer 132A and the profile of the recessed portion 134R of the selectiondevice 134A may be changed based on materials of the variable resistancelayer 132A and the selection device 134A, heights of the variableresistance layer 132A and the selection device 134A, and an etch recipeapplied to the isotropic etching process for the variable resistancelayer 132A and the selection device 134A.

According to an exemplary embodiment of the present inventive concept,when a first isotropic etching process for the variable resistance layer132A and a second isotropic etching process for the selection device134A are separately performed, the profile of the recessed portion 132Rof the variable resistance layer 132A may differ from the profile of therecessed portion 134R of the selection device 134A. For example, when anetch rate of the first isotropic etching process differs from an etchrate of the second isotropic etching process, for example, the side wallof the variable resistance layer 132A may include the recessed portion132R which is approximately vertically planar, and a slope angle of therecessed portion 134R of the selection device 134A may be greater thanillustrated in FIG. 6. According to an exemplary embodiment of thepresent inventive concept, even when the isotropic etching process forthe variable resistance layer 132A and the isotropic etching process forthe selection device 134A are substantially simultaneously performed,the profile of the recessed portion 132R of the variable resistancelayer 132A may differ from the profile of the recessed portion 134R ofthe selection device 134A, based on materials and/or a height differenceof the variable resistance layer 132A and the selection device 134A.

FIG. 7 is a cross-sectional view illustrating a memory device accordingto an exemplary embodiment of the present inventive concept. Referringto FIG. 7, like reference numerals may refer to like componentsdescribed with reference to FIGS. 1 to 6 and thus duplicativedescriptions may be omitted.

FIG. 7 illustrates a cross-sectional view corresponding to across-sectional view taken along line X1-X1′ of FIG. 2. Except for ashape of each of a first capping layer 142B and a second capping layer144B, a memory device 100 b described with reference to FIG. 7 may besubstantially the same as the memory device 100 described with referenceto FIGS. 2 to 4.

Referring to FIG. 7, a plurality of memory cell pillars 130B may eachinclude a variable resistance layer 132B, having a second width W2B in asecond direction (e.g., a Y direction), and a selection device 134Bhaving a third width W3B different from the second width W2B. A fourthwidth W4B of the first capping layer 142B, contacting the variableresistance layer 132B, in the second direction (e.g., the Y direction)may differ from a fifth width W5B of the second capping layer 144B,contacting the selection device 134B, in the second direction.

For example, the second width W2B of the variable resistance layer 132Bmay be less than the third width W3B of the selection device 134B. Whenthe second width W2B of the variable resistance layer 132B is less thanthe third width W3B of the selection device 134B, a heat collectioneffect may increase, and thus, a reset current of the memory device 100Bmay be reduced (e.g., or a “reset” operation may be performed at arelatively low reset current). When the second width W2B of the variableresistance layer 132B is relatively small, thermal crosstalk (e.g., orthermal interference) in which heat which is generated in a “write”operation for an arbitrary variable resistance layer 132B and which mayaffect an adjacent variable resistance layer 132B, may be reduced orprevented.

However, exemplary embodiments of the present inventive concept are notlimited thereto, and the second width W2B of the variable resistancelayer 132B may be greater than the third width W3B of the selectiondevice 134B.

FIG. 8 is a cross-sectional view illustrating a memory device accordingto an exemplary embodiment of the present inventive concept. FIG. 8illustrates a cross-sectional view corresponding to a cross-sectionalview taken along line X1-X1′ of FIG. 2.

Referring to FIG. 8, in a memory device 100 c according to an exemplaryembodiment of the present inventive concept, a plurality of memory cellpillars 130C may each include an insulation liner 146 disposed between avariable resistance layer 132C and the first capping layer 142. Theinsulation liner 146 may extend to a bottom of the first capping layer142 and a bottom of a top electrode TE and may also extend to a top ofthe first capping layer 142 and a top of a middle electrode ME. Theinsulation liner 146 need not be disposed between a selection device134C and a second capping layer 144.

In an exemplary embodiment of the present inventive concept, theinsulation liner 146 may include silicon oxynitride or silicon nitrideand may have a sixth width W6C of from about 1 nm to about 20 nm.However, exemplary embodiments of the present inventive concept are notlimited thereto.

In a process of forming the plurality of memory cell pillars 130Caccording to an exemplary embodiment of the present inventive concept,the insulation liner 146 having a predetermined thickness may be firstformed on a side wall of the variable resistance layer 132C, and then,the first and second capping layers 142 and 144 may be substantiallysimultaneously formed on the insulation liner 146 and a selection device134C. A fourth width W4C of the first capping layer 142 may besubstantially the same as a fifth width W5C of the second capping layer144. In this case, by adjusting the sixth width W6C of the insulationliner 146, a second width W2C of the variable resistance layer 132C maybe formed less than a third width W3C of the selection device 134C.Thus, the heat collection effect in the plurality of memory cell pillars130C may be increased, and thus, a reset current of the memory device100C may be reduced.

However, exemplary embodiments of the present inventive concept are notlimited thereto. According to an exemplary embodiment of the presentinventive concept, the first capping layer 142 may be first formed onthe insulation liner 146, and then, the second capping layer 144 may beformed on the selection device 134C.

According to an exemplary embodiment of the present inventive concept,when the insulation liner 146 might be formed on only the side wall ofthe variable resistance layer 132C. According to an exemplary embodimentof the present inventive concept, when the variable resistance layer132C is disposed under the selection device 134C, the insulation liner146 may be formed on only a side wall of the selection device 134C. Inan exemplary embodiment of the present inventive concept, the variableresistance layer 132C may be disposed on the selection device 134C, andthe insulation liner 146 may be formed on only the side wall of theselection device 134C. The insulation liner 146 may be formed on all theside walls of the variable resistance layer 132C and the selectiondevice 134C.

FIG. 9 is a cross-sectional view illustrating a memory device accordingto an exemplary embodiment of the present inventive concept. FIG. 9illustrates a cross-sectional view corresponding to a cross-sectionalview taken along line X1-X1′ of FIG. 2.

Referring to FIG. 9, in a memory device 100D according to an exemplaryembodiment of the present inventive concept, an air spacer AS may beformed in a plurality of first insulation patterns 150A. The air spacerAS may also be formed in a plurality of second insulation patterns 160(see, e.g., the second insulation patterns 160 illustrated in FIG. 2).

In an exemplary embodiment of the present inventive concept, theplurality of first insulation patterns 150A may include an insulatingmaterial such as silicon oxide. For example, the insulating materialmight not fully fill a space between the memory cell pillars 130 in aprocess of forming the plurality of first insulation patterns 150A, andthus the air spacer AS may be formed in the insulating material.

In an exemplary embodiment of the present inventive concept, theplurality of first insulation patterns 150A may have a relatively thinthickness and may conformally cover a side wall of each of the memorycell pillars 130. A sacrificial layer filling the space between thememory cell pillars 130 may be formed on the plurality of firstinsulation patterns 150A, and then, the air spacer AS may be formed inthe plurality of first insulation patterns 150A by selectively removingthe sacrificial layer through an aching process and/or a strip process.

The air spacer AS may be lower in dielectric constant than the first andsecond capping layers 142 and 144. Thus, RC delay which may occur indriving the memory device 100D may be reduced, and thus the memorydevice 100D may operate at a relatively high speed.

FIG. 10 is a perspective view illustrating a memory device according toan exemplary embodiment of the present inventive concept. FIG. 11 is across-sectional view taken along line X1-X1′ and line Y1-Y1′ of FIG. 10.FIG. 12 is an equivalent circuit diagram of a memory device according toan exemplary embodiment of the present inventive concept.

Referring to FIGS. 10 to 12, a memory device 200 may include bottom wordlines 110 (e.g., word lines WL11 and WL12), which may extend along afirst direction (e.g., an X direction), and top word lines 210 (e.g.,word lines WL21 and WL22) which extend along the first direction (e.g.,the X direction in FIG. 10) and are spaced apart from the bottom wordlines 110 in a third direction (e.g., a Z direction) perpendicular tothe first direction above the bottom word lines 110. The memory device200 may include common bit lines 120 (e.g., bit lines BL1 to BL4) whichextend along a second direction (e.g., a Y direction) and are spacedapart from the top word lines 210 and the bottom word lines 110 in thethird direction.

A first memory unit 130 (MC1) may be disposed between the common bitlines 120 and the bottom word lines 110. A second memory unit 230 (MC2)may be disposed between the common bit lines 120 and the top word line210. A selection device SW and a variable resistance layer ME may beserially connected to each other in the first memory unit 130 (MC1) andthe second memory unit 230 (MC2).

Referring to FIG. 11, a plurality of insulation patterns 260 may berespectively disposed between the first and second memory units 130 and230.

The first memory unit 130 (MC1) and the second memory unit 230 (MC2) mayhave characteristics similar to those of the memory cell pillars 130described above with reference to FIGS. 2 to 4.

The first memory unit 130 may include a first bottom electrode BE1, afirst selection device 134, a first middle electrode ME1, a firstvariable resistance layer 132, and a first top electrode TE1 which aresequentially disposed at a cross point between the common bit lines 120and the bottom word lines 110. A first capping layer 142X and 142Y maybe formed on a side wall of the first variable resistance layer 132, anda second capping layer 144X and 144Y may be formed on a side wall of thefirst selection device 134. According to an exemplary embodiment of thepresent inventive concept, the positions of the first selection device134 and the first variable resistance layer 132 may be reversed in thefirst memory unit 130.

The second memory unit 230 may include a second bottom electrode BE2, asecond selection device 234, a second middle electrode ME2, a secondvariable resistance layer 232, and a second top electrode TE2 which aresequentially disposed at a cross point between the common bit lines 120and the top word lines 210. A third capping layer 242 including cappinglayers 242X and 242Y may be formed on a side wall of the second variableresistance layer 232, and a fourth capping layer 244 including cappinglayers 244X and 244Y may be formed on a side wall of the secondselection device 234. According to an exemplary embodiment of thepresent inventive concept, the dispositions of the second selectiondevice 234 and the second variable resistance layer 232 may be reversedin the second memory unit 230.

Referring to FIGS. 10 to 12, the memory device 200 may have across-point array structure where the first memory unit 130 and thesecond memory unit 230 are respectively stacked under and on the commonbit line 120 according to an exemplary embodiment of the presentinventive concept. However, exemplary embodiments of the presentinventive concept are not limited thereto. According to an exemplaryembodiment of the present inventive concept, the memory device 200 mayhave a structure in which the first memory unit 130 and the secondmemory unit 230 are respectively stacked under and on a common wordline.

According to an exemplary embodiment of the present inventive concept,an insulation layer may be formed on the top word line 210, and astacked structure including the bottom word line 110, the common bitline 120, the top word line 210, the first memory unit 130, and thesecond memory unit 230 may be formed on the insulation layer. As anexample, two or more the stacked structures may be disposed in the thirddirection (e.g., the Z direction) with the insulation layer disposedbetween the two or more stacked structures.

FIG. 13 is a perspective view illustrating a memory device according toan exemplary embodiment of the present inventive concept. FIG. 14 is across-sectional view taken along line X1-X1 of FIG. 13.

Referring to FIGS. 13 and 14, a memory device 300 may include a drivingcircuit area 310 in a first level above a substrate 102, and a memorycell array area MCA in a second level above the substrate 102.

The term “level” denotes a height in a vertical direction (e.g., a Zdirection) from the substrate 102. The first level above the substrate102 may be closer to the substrate 102 than the second level above thesubstrate 102.

The driving circuit area 310 may include areas where peripheral circuitsor driving circuits for driving memory cells in the memory cell arrayarea MCA are disposed. For example, the peripheral circuits disposed inthe driving circuit area 310 may be circuits for processing datainput/output to/from the memory cell array area MCA at a relatively highspeed. For example, the peripheral circuits may be a page buffer, alatch circuit, a cache circuit, a column decoder, a sense amplifier, adata in/out circuit, and/or a row decoder.

An active area AC for driving circuits may be defined on the substrate102 by an isolation layer 104. A plurality of transistors TR configuringthe driving circuit area 310 may be formed in the active area AC of thesubstrate 102. The plurality of transistors TR may each include a gateG, a gate insulation layer GD, and a source/drain area SD. Side walls ofthe gate G may be covered by an insulation spacer 106, and an etchstopper 108 may be formed on the gate G and the insulation spacer 106.The etch stopper 108 may include an insulating material such as siliconnitride, or silicon oxynitride.

A plurality of insulating interlayers 312A, 312B and 312C may besequentially stacked on the etch stopper 108. The plurality ofinsulating interlayers 312A, 312B and 312C may each include siliconoxide, silicon oxynitride, and/or silicon nitride.

The driving circuit area 310 may include a multilayer wiring structure314 electrically connected to the plurality of transistors TR. Themultilayer wiring structure 314 may be insulated from the plurality ofinsulating interlayers 312A, 312B and 312C.

The multilayer wiring structure 314 may include a first contact 316A, afirst wiring layer 318A, a second contact 316B, and a second wiringlayer 318B which are sequentially stacked on the substrate 102 and areelectrically connected to each other. In an exemplary embodiment of thepresent inventive concept, the first wiring layer 318A and the secondwiring layer 318B may each include metal, conductive metal nitride,metal silicide, or a combination thereof. For example, the first wiringlayer 318A and the second wiring layer 318B may each include aconductive material such as tungsten (W), molybdenum (Mo), titanium(Ti), cobalt (Co), tantalum (Ta), nickel (Ni), tungsten silicide,titanium silicide, cobalt silicide, or nickel silicide.

Referring to FIG. 14, according to an exemplary embodiment of thepresent inventive concept, the multilayer wiring structure 314 may havea two-layer wiring structure including the first wiring layer 318A andthe second wiring layer 318B, but exemplary embodiments of the presentinventive concept are not limited thereto. For example, the multilayerwiring structure may have a multilayer wiring structure including threeor more layers, based on a layout of the driving circuit area 310 andthe kind and arrangement of the gate G.

A top insulating interlayer 320 may be formed on the plurality ofinsulating interlayers 312A to 312C. The memory cell array area MCA maybe disposed on the top insulating interlayer 320. The memory devices100, 100A, 100B, 100C, 100D or 200 described in more detail above withreference to FIGS. 1 to 12 or a combination thereof may be disposed inthe memory cell array area MCA.

A wiring structure connected between the memory cell array area MCA andthe driving circuit area 310 may pass through the top insulatinginterlayer 320.

In the memory device 300 according to an exemplary embodiment of thepresent inventive concept, since the memory cell array area MCA may bedisposed on the driving circuit area 310, a degree of integration of thememory device 300 may be increased.

FIGS. 15A to 150 are cross-sectional views illustrating a method ofmanufacturing a memory device according to an exemplary embodiment ofthe present inventive concept.

A method of manufacturing the memory device 100 will be described inmore detail below with reference to FIGS. 15A to 150. A cross-sectionalview corresponding to a cross-sectional view taken along line X1-X1′ ofFIG. 2 and a cross-sectional view corresponding to a cross-sectionalsurface taken along line Y1-Y1′ of FIG. 2 will be described in moredetail below with reference to 15A to 150. Referring to FIGS. 15A to150, like reference numerals may refer to like components described withreference to FIGS. 1 to 14 and thus duplicative descriptions may beomitted.

Referring to FIG. 15A, the insulating interlayer 105 may be formed onthe substrate 102, and a first conductive layer 110P may be formed onthe insulating interlayer 105. A stacked structure CPS, in which apreliminary bottom electrode layer PBE, a preliminary selection devicelayer 134P, a preliminary middle electrode layer PME, a preliminaryvariable resistance layer 132P, and a preliminary top electrode layerPTE are sequentially stacked, for forming a cross-point array, may beformed on the first conductive layer 110P.

A first mask pattern 410 may be formed on the stacked structure CPS.

The first mask pattern 410 may include a plurality of line patterns thatextend in a first direction (e.g., the X direction). The first maskpattern 410 may have a single layer or a multilayer structure in which aplurality of layers are stacked. For example, the first mask pattern 410may include a photoresist pattern, a silicon oxide pattern, a siliconnitride pattern, a silicon oxynitride pattern, a polysilicon pattern, ora combination thereof, but exemplary embodiments of the presentinventive concept are not limited thereto. In an exemplary embodiment ofthe present inventive concept, the first mask pattern 410 may includevarious materials.

Referring to FIG. 15B, by using the first mask pattern 410 as an etchmask, the preliminary top electrode PTE and the preliminary variableresistance layer 132P may be sequentially anisotropic-etched to separatethe preliminary top electrode layer PTE into a plurality of topelectrode lines TEL and separate the preliminary variable resistancelayer 132P into a plurality of variable resistance layer lines 132L.

Thus, the plurality of top electrode lines TEL and the plurality ofvariable resistance layer lines 132L extending in the first direction(e.g., the X direction) may be formed, and a plurality of first gaps GX1extending in the first direction (e.g., the X direction) may berespectively formed between the plurality of top electrode lines TEL andthe plurality of variable resistance layer lines 132L.

As the plurality of first gaps GX1 are formed, a portion of a top of thepreliminary middle electrode layer PME may be exposed to a bottomportion of each of the first gaps GX1. Referring to FIG. 15B, theportion of the top of the preliminary middle electrode layer PME exposedto each of the first gaps GX1 may be recessed, but exemplary embodimentsof the present inventive concept are not limited thereto.

Referring to FIG. 15C, side portions of the plurality of variableresistance layer lines 132L may be removed by a predetermined width byperforming an isotropic etching process on side walls of the variableresistance layer lines 132L exposed by the plurality of first gaps GX1.

The isotropic etching process may be an etching process based on anetching condition where an etching rate is sufficiently high to form theplurality of variable resistance layer lines 132L. For example, thepreliminary middle electrode layer PME and the plurality of topelectrode lines TEL may be etched a relatively small amount in theisotropic etching process, but may be etched at an etching rate farlower than an etching rate at which the plurality of variable resistancelayer lines 132L are etched.

Since the plurality of variable resistance layer lines 132L are etchedto the predetermined width while the preliminary middle electrode layerPME and the plurality of top electrode lines TEL are not etched in theisotropic etching process, a first undercut area 132XU may be formed ina portion adjacent to each of side walls of the plurality of variableresistance layer lines 132L under the plurality of top electrode linesTEL.

In an exemplary embodiment of the present inventive concept, theisotropic etching process may include a wet etching process and a dryetching process which use at least one of HBr, Cl₂, or F₂ as an etchant.For example, the isotropic etching process may be a reactive ion etchingprocess or a reactive radical etching process, which uses an HBr gas asan etchant. For example, the isotropic etching process may be a wetetching process which uses a LAL solution as an etchant.

A profile of a side wall of each of the variable resistance layer lines132L may be changed based on an etch rate of the isotropic etchingprocess and/or a material of the variable resistance layer lines 132L.For example, the plurality of variable resistance layer lines 132L mayeach have a side wall profile which is vertically planar, or may have arounded side wall profile. For example, according to an exemplaryembodiment of the present inventive concept, when the side walls of theplurality of variable resistance layer lines 132L have a shape which isrounded and is recessed toward the insides of the plurality of variableresistance layer lines 132L, the memory device 100A may be manufactured.

Referring to FIG. 15D, a first preliminary capping layer 142L1 may beformed on the stacked structure CPS. The first preliminary capping layer142L1 may be conformally formed on sides walls of the top electrodelines TEL and the variable resistance layer lines 132L and a top of thepreliminary middle electrode layer PME, which are exposed by theplurality of first gaps GX1, in the stacked structure CPS.

In an exemplary embodiment of the present inventive concept, the firstpreliminary capping layer 142L1 may be include silicon nitride orsilicon oxynitride. For example, the first preliminary capping layer142L1 may be formed by a chemical vapor deposition (CVD) process, anatomic layer deposition (ALD) process, or a plasma enhanced CVD (PECVD)process. The first preliminary capping layer 142L1 may be formed to athickness of from about 2 nm to about 50 nm.

In an exemplary embodiment of the present inventive concept, the firstpreliminary capping layer 142L1 may fill the first undercut area 132XU.However, exemplary embodiments of the present inventive concept are notlimited thereto.

Referring to FIG. 15E, a plurality of first capping lines 142XP may beformed on side walls of the variable resistance layer lines 132L byetching back the first preliminary capping layer 142L1 in the pluralityof first gaps GX1 until the top of the preliminary middle electrodelayer PME is exposed.

Only a portion of the first preliminary capping layer 142L1 filled intothe first undercut area 132XU may remain while a portion of the firstpreliminary capping layer 142L1 disposed in each of the first gaps GX1is being removed in the etchback process, and thus, the plurality offirst capping lines 142XP may be formed. Side walls of the first cappinglines 142XP may contact the side walls of the variable resistance layerlines 132L, and tops and bottoms of the first capping lines 142XP maycontact bottoms of the top electrode lines TEL and tops of a pluralityof middle electrode lines MEL.

A portion of the first preliminary capping layer 142L1 disposed on thefirst mask pattern 410 may be removed by the etchback process, and thetop of the first mask pattern 410 may be exposed. The plurality of firstcapping lines 142XP may extend along the first direction (e.g., the Xdirection) both side walls of each of the variable resistance layerlines 132L.

Referring to FIG. 15F, by using the first mask pattern 410 as an etchmask, the preliminary middle electrode layer PME and the preliminaryselection device layer 134P may be sequentially anisotropic-etched toseparate the preliminary middle electrode layer PME into a plurality ofmiddle electrode lines MEL and separate the preliminary selection devicelayer 134P into a plurality of selection device layer lines 134L.

Thus, the plurality of middle electrode lines MEL and the plurality ofselection device layer lines 134L extending in the first direction(e.g., the X direction) may be formed, and a bottom portion of each ofthe first gaps GX1 may extend to between the plurality of middleelectrode lines MEL and the plurality of selection device layer lines134L.

In the anisotropic etching process of forming the plurality of middleelectrode lines MEL and the plurality of selection device layer lines134L, the side walls of the variable resistance layer lines 132L may becovered by the plurality of first capping lines 142XP and thus the sidewalls need not be exposed. Since the side walls of the variableresistance layer lines 132L are not exposed to the etching atmosphere,an occurrence of damage to the variable resistance layer lines 132Lduring the etching process may be reduced or prevented.

Side portions of the selection device layer lines 134L may be removed bya predetermined width by performing an isotropic etching process on sidewalls of the selection device layer lines 134L exposed by the pluralityof first gaps GX1.

The isotropic etching process may be an etching process based on anetching condition where an etching rate is sufficiently high for theplurality of selection device layer lines 134L. For example, thepreliminary bottom electrode layer PBE, the plurality of top electrodelines TEL, and the plurality of middle electrode lines MEL may be etchedin the isotropic etching process, but may be etched at an etching ratefar lower than an etching rate at which the plurality of selectiondevice layer lines 134L are etched.

Since the plurality of selection device layer lines 134L are etched tothe predetermined width while the preliminary bottom electrode layer PBEand the plurality of middle electrode lines MEL are not etched in theisotropic etching process, a second undercut area 134XU may be formed ina portion adjacent to each of side walls of the selection device layerlines 134L under the plurality of middle electrode lines MEL.

In the isotropic etching process, the side walls of the variableresistance layer lines 132L may be covered by the plurality of firstcapping lines 142XP and thus the side walls need not be exposed to theplurality of first gaps GX1. Since the side walls of the variableresistance layer lines 132L are not exposed to the etching atmosphere,an occurrence of damage to the variable resistance layer lines 132L inthe etching process may be reduced or prevented.

The isotropic etching process for the variable resistance layer lines132L may be similar to the isotropic etching process, described in moredetail above with reference to FIG. 15C.

Referring to FIG. 15G, a second preliminary capping layer 144L1 may beformed on the stacked structure CPS. The second preliminary cappinglayer 144L1 may be conformally formed on sides walls of the topelectrode lines TEL, the first capping lines 142XP, the middle electrodelines MEL, and the selection device layer lines 134L and a top of thepreliminary middle electrode layer PME, which are exposed by theplurality of first gaps GX1, in the stacked structure CPS.

In an exemplary embodiment of the present inventive concept, the secondpreliminary capping layer 144L1 may include silicon nitride or siliconoxynitride and may be formed by a CVD process, an ALD process, or aPECVD process. The second preliminary capping layer 144L1 may be formedto a thickness of from about 2 nm to about 50 nm. However, exemplaryembodiments of the present inventive concept are not limited thereto.

In an exemplary embodiment of the present inventive concept, the secondpreliminary capping layer 144L1 may fill the second undercut area 134XU.However, exemplary embodiments of the present inventive concept are notlimited thereto.

Referring to FIG. 15H, a plurality of second capping lines 144XP may beformed on side walls of the selection device layer lines 134L by etchingback the second preliminary capping layer 144L1 in the plurality offirst gaps GX1 until the top of the preliminary bottom electrode layerPBE is again exposed.

Only a portion of the second preliminary capping layer 144L1 filled intothe second undercut area 134XU may remain while a portion of the secondpreliminary capping layer 144L1 disposed in each of the first gaps GX1are being removed in the etchback process, and thus, the plurality ofsecond capping lines 144XP may be formed.

A portion of the second preliminary capping layer 144L1 disposed on thefirst mask pattern 410 may be removed by the etchback process, and thetop of the first mask pattern 410 may be exposed. The plurality ofsecond capping lines 144XP may extend along the first direction (e.g.,the X direction) on side walls of each of the selection device layerlines 134L.

Referring to FIG. 15I, by using the first mask pattern 410 as an etchmask, the preliminary bottom electrode layer PBE and the firstconductive layer 110P may be sequentially anisotropic-etched to separatethe preliminary bottom electrode layer PBE into a plurality of bottomelectrode lines BEL and separate the first conductive layer 110P into aplurality of word lines 110.

The side walls of the variable resistance layer lines 132L may becovered by the first capping lines 142XP, and the side walls of theselection device layer lines 134L may be covered by the second cappinglines 144XP. Thus, the variable resistance layer lines 132L and theselection device layer lines 134L may be prevented from being exposed tothe etching atmosphere and damage to the variable resistance layer lines132L and the selection device layer lines 134L due to the exposure maybe prevented.

In the anisotropic etching process of forming the plurality of bottomelectrode lines BEL and the plurality of word lines 110, a plurality ofstacked lines CPL which are spaced apart from each other by theplurality of first gaps GX1 and extend in the first direction (e.g., theX direction) may be formed on the substrate 102.

Subsequently, the first mask pattern 410 may be removed.

Referring to FIG. 15J, a first insulation layer 150P filling each of thefirst gaps GX1 may be formed. For example, the first insulation layer150P may be formed on the plurality of stacked lines CPL and theinsulating interlayer 105 by filling the plurality of first gaps GX1with an insulating material and planarizing a top of the insulationmaterial until tops of the stacked lines CPL are exposed.

In an exemplary embodiment of the present inventive concept, the firstinsulation layer 150P may include a material which is lower indielectric constant than the first and second capping lines 142L and144L. For example, the first insulation layer 150P may include siliconoxide such as BPSG, PSG, USG, FSG, SOG, FOX, TEOS, PE-TEOS, HDP-CVDoxide, FSG, SiOC, or the like. The first insulation layer 150P mayinclude one kind of insulation layer or a plurality of insulationlayers. However, exemplary embodiments of the present inventive conceptare not limited thereto.

In an exemplary embodiment of the present inventive concept, the airspacer AS may be formed in the first insulation layer 150P. Thus, thememory device 100D may be manufactured.

When the air spacer AS is formed in the first insulation layer 150P, thefirst insulation layer 150P may include silicon oxide. According to anexemplary embodiment of the present inventive concept, since theplurality of first gaps GX1 are not fully filled in a process of formingthe first insulation layer 150P, the air spacer AS may be formed in thefirst insulation layer 150P. According to another exemplary embodimentof the present inventive concept, the first insulation layer 150P whichhas a relatively thin thickness and conformally covers inner walls ofthe first gaps GX1 may be formed and a sacrificial layer which fills theinsides of the first gaps GX1 on the first insulation layer 150P may beformed, and then, the air spacer AS may be formed in the firstinsulation layer 150P by selectively removing the sacrificial layerthrough an ashing process and/or a strip process.

A second conductive layer 120P may be formed on the first insulationlayer 150P and the plurality of stacked lines CPL. The second conductivelayer 120P may be similar to the first conductive layer 110P.

Referring to FIG. 15K, a second mask pattern 420 may be formed on thesecond conductive layer 120P. The second mask pattern 420 may include aplurality of line patterns that extend in a second direction (e.g., a Ydirection). The second mask pattern 420 may have a single layerstructure or a multilayer structure in which a plurality of layers isstacked.

By using the second mask pattern 420 as an etch mask, the secondconductive layer 120P, the plurality of top electrode lines TEL, and theplurality of variable resistance layer lines 132L may be sequentiallyanisotropic-etched to separate the second conductive layer 120P into aplurality of bit lines 10, separate each of the top electrode lines TELinto a plurality of top electrodes TE, and separate each of the variableresistance layer lines 132L into a plurality of variable resistancelayers 132.

A plurality of second gaps GY1 extending along the second direction(e.g., the Y direction) may be formed by the anisotropic process. Theplurality of top electrodes TE and the plurality of variable resistancelayers 132 may be spaced apart from each other along the first directionand the second direction. Each of the first capping lines 142XP disposedon the side walls of the variable resistance layers 132 may be separatedinto first portions 142X of the first capping layers 142.

Side portions of the variable resistance layers 132 may be removed by apredetermined width by performing an isotropic etching process on sidewalls of the variable resistance layers 132 exposed by the plurality ofsecond gaps GY1. Thus, a third undercut area 132YU may be formed in aportion adjacent to each of the side walls of the variable resistancelayers 132 under the plurality of top electrodes TE. The first portions142X of the first capping layers 142 need not be removed in theisotropic etching process.

Referring to FIG. 15L, a third preliminary capping layer may beconformally formed on the stacked structure CPS, and the second portion142Y of the first capping layer 142 may be formed on the side wall ofeach of the variable resistance layers 132 by etching back the thirdpreliminary capping layer in each of the second gaps GY1 until the topsof the middle electrode lines MEL are exposed.

The second portion 142Y of the first capping layer 142 may cover theside wall of each of the variable resistance layers 132 exposed by theplurality of second gaps GY1. The second portion 142Y of the firstcapping layer 142 together with the first portion 142X may surround theside wall of each of the variable resistance layers 132.

Referring to FIG. 15M, by using the second mask pattern 420 as an etchmask, the plurality of middle electrode lines MEL and the plurality ofselection device layer lines 134L may be sequentially anisotropic-etchedto separate each of the middle electrode lines MEL into a plurality ofmiddle electrodes ME and separate each of the selection device layerlines 134L into a plurality of selection devices 134.

The plurality of middle electrodes ME and the plurality of selectiondevices 134 may be spaced apart from each other along the firstdirection and the second direction. Each of the second capping lines144XP disposed on the side walls of the selection devices 134 may beseparated into third portions 144X of a plurality of second cappinglayers 144.

The side walls of the selection devices 134 may be removed by apredetermined width by performing an isotropic etching process on theside walls of the selection devices 134 exposed by the plurality ofsecond gaps GY1. A fourth undercut area 134YU may be formed in a portionadjacent to each of the side walls of the selection devices 134 underthe plurality of middle electrodes ME.

Referring to FIG. 15N, a fourth preliminary capping layer may beconformally formed on the stacked structure CPS, and the fourth portion144Y of the second capping layer 144 may be formed on the side wall ofeach of the selection devices 134 by etching back the fourth preliminarycapping layer in each of the second gaps GY1 until the tops of thebottom electrode lines BEL are exposed.

The fourth portion 144Y of the second capping layer 144 may cover theside wall of each of the selection devices 134 exposed by the pluralityof second gaps GY1. The fourth portion 144Y of the second capping layer144 together with the third portion 144X may surround the side wall ofeach of the selection devices 134.

Referring to FIG. 15O, by using the second mask pattern 420 as an etchmask, the plurality of bottom electrode lines BEL may be anisotropicallyetched to separate each of the bottom electrode lines BEL into aplurality of bottom electrodes BE. Each of the stacked lines CPL may beseparated into a plurality of memory pillars 130, which are spaced apartfrom each other in the first direction and the second direction, by theanisotropic etching process. The first insulation layer 150P may beseparated into a plurality of first insulation patterns 150, which arespaced apart from each other in the first direction and the seconddirection between the plurality of memory cell pillars 130, by theanisotropic etching process.

A plurality of second insulation patterns 160 filling the plurality ofsecond gaps GY1 may be formed on the plurality of bit lines 120, theplurality of memory cell pillars 130, and the plurality of firstinsulation patterns 150 by filling the plurality of second gaps GY1 withan insulating material and planarizing a top of the insulation material.The plurality of second insulation patterns 160 may extend along thesecond direction (e.g., the Y direction).

In an exemplary embodiment of the present inventive concept, theplurality of second insulation patterns 160 may each include a materialwhich is lower in dielectric constant than the first and second cappinglayers 142 and 144. For example, the plurality of second insulationpatterns 160 may each include a silicon oxide, such as, BPSG, PSG, USG,FSG, SOG, FOX, TEOS, PE-TEOS, HDP-CVD oxide, FSG, or SiOC.

According to an exemplary embodiment of the present inventive concept,in a process of forming the plurality of memory cell pillars 130 (forexample, a process of etching the plurality of memory cell pillars 130,a process of etching the word lines 110 or the bit lines 120, or aprocess of forming the plurality of insulation patterns 150 and 160),when the variable resistance layer 132 including the phase materiallayer and the selection device 134 including the material having the OTScharacteristic are exposed to an atmosphere (e.g., air) of the processfor example, the variable resistance layer 132 and the selection device134 may be damaged. A passivation layer including silicon nitride maysurround a side wall of each of the plurality of memory cell pillars130, and thus damage to the cell pillars 130 may be reduced orprevented. However, in a memory device including a cross-pointstructure, as a width of each of the memory cell pillars 130 is reduced,an interval between the memory cell pillars 130 is also reduced. Thus,the passivation layer may substantially fully fill the interval betweenthe memory cell pillars 130, and a parasitic capacitance increases dueto the passivation layer which has a high dielectric constant generally,may cause a relatively large RC delay in driving the memory device.

In the method of manufacturing the memory device 100 according to anexemplary embodiment of the present inventive concept, the cappinglayers 142 and 144 having a relatively thin thickness may be disposed ononly the side walls of the variable resistance layer 132 and theselection device 134 by the isotropic etching process, and the pluralityof insulation patterns 150 and 160 may be disposed between the memorycell pillars 130. The plurality of insulation patterns 150 and 160 mayinclude a material having a dielectric constant which is lower than thatof each of the capping layers 142 and 144. Thus, RC delay which mayoccur in driving the memory device 100 may be reduced or eliminated,thus enabling the memory device 100 to operate at a relatively highspeed.

In the method of manufacturing the memory device 100 according to anexemplary embodiment of the present inventive concept, since the firstand second capping layers 142 and 144 may be disposed on only the sidewalls of the variable resistance layers 132 and the selection devices134, the variable resistance layers 132 and the selection devices 134may be prevented from being exposed or damaged in a process of thebottom layer or a process of manufacturing the plurality of insulationpatterns 150 and 160. Thus, the memory device 100 manufactured by themanufacturing method may have increased reliability.

FIGS. 16A to 16G are cross-sectional views illustrating a method ofmanufacturing a memory device according to an exemplary embodiment ofthe present inventive concept. Referring to FIGS. 16A to 16G, likereference numerals may refer to like components described with referenceto FIGS. 15A to 150 and thus duplicative descriptions may be omitted.

Referring to FIG. 16A, the first mask pattern 410 may be formed on thestacked structure CPS. The stacked structure CPS may beanisotropic-etched by using the first mask pattern 410 as an etch maskto respectively separate the preliminary top electrode layer PTE, thepreliminary variable resistance layer 132P, the preliminary middleelectrode layer PME, and the preliminary selection device layer 134Pinto a plurality of top electrode lines TEL, a plurality of variableresistance layer lines 132L, a plurality of middle electrode lines MEL,and a plurality of selection device layer lines 134L, respectively.

Thus, a plurality of first gaps GX1A extending in a first direction(e.g., the X direction) may be respectively formed between the pluralityof top electrode lines TEL, the plurality of variable resistance layerlines 132L, the plurality of middle electrode lines MEL, and theplurality of selection device layer lines 134L extending in the firstdirection (e.g., the X direction).

Referring to FIG. 16B, side portions of the variable resistance layerlines 132L and side portions of the selection device layer lines 134Lmay be removed by a predetermined width by performing an isotropicetching process on side walls of the variable resistance layer lines132L and side walls of the selection device layer lines 134L exposed bythe plurality of first gaps GX1A.

In the isotropic etching process, the plurality of variable resistancelayer lines 132L and the plurality of selection device layer lines 134Lmay be etched by the predetermined width while the plurality of topelectrode lines TEL and the plurality of middle electrode lines MEL arenot etched. Thus, a first undercut area 132XU may be formed in a portionadjacent to each of side walls of the variable resistance layer lines132L under the plurality of top electrode lines TEL, and a secondundercut area 134XU may be formed in a portion adjacent to each of sidewalls of the selection device layer lines 134L under the plurality ofmiddle electrode lines MEL.

A width of the first undercut area 132XU and a width of the secondundercut area 134XU may be changed based on the isotropic etchingprocess conditions and/or a material of each of the variable resistancelayer lines 132L and the selection device layer lines 134L.

In an exemplary embodiment of the present inventive concept, in theisotropic etching process, an etching rate at which the plurality ofvariable resistance layer lines 132L are etched may be similar to anetching rate at which the plurality of selection device layer lines 134Lare etched. For example, when the plurality of variable resistance layerlines 132L and the plurality of selection device layer lines 134L eachinclude a chalcogenide material, the plurality of variable resistancelayer lines 132L and the plurality of selection device layer lines 134Lmay be etched at similar etching rates in the isotropic etching process.In the isotropic etching process, an amount by which side portions ofthe variable resistance layer lines 132L are removed may be similar toan amount by which side portions of the selection device layer lines134L are removed, and the width of the first undercut area 132XU may besimilar to the width of the second undercut area 134XU. Thus, the memorydevice 100 may be manufactured.

In an exemplary embodiment of the present inventive concept, theisotropic etching process may use an etching condition where an etchingrate at which the plurality of variable resistance layer lines 132L areetched may differ from an etching rate at which the plurality ofselection device layer lines 134L are etched. Thus, the width of thefirst undercut area 132XU may differ from the width of the secondundercut area 134XU. Thus, the memory device 100B may be manufactured.

Referring to FIG. 16C, a fifth preliminary capping layer 140L1 may beconformally formed on the plurality of top electrode lines TEL, theplurality of variable resistance layer lines 132L, the plurality ofmiddle electrode lines MEL, the plurality of selection device layerlines 134L, and a preliminary bottom electrode layer PBE. The fifthpreliminary capping layer 140L1 may fill the first undercut area 132XUand the second undercut area 134XU.

Referring to FIG. 16D, by etching back the fifth preliminary cappinglayer 140L1 in each of the first gaps GX1A until a top of thepreliminary bottom electrode layer PBE is exposed, a plurality of firstcapping lines 142XP may be formed on side walls of the variableresistance layer lines 132L, and a plurality of second capping lines144XP may be formed on side walls of the selection device layer lines134L.

When the width of the first undercut area 132XU is substantially thesame as that of the second undercut area 134XU, a fourth width W4 ofeach of the first capping lines 142XP may be substantially the same as afifth width W5 of each of the second capping lines 144XP. However,exemplary embodiments of the present inventive concept are not limitedthereto. According to an exemplary embodiment of the present inventiveconcept, the fourth width W4 of each of the first capping lines 142XPmay be different from the fifth width W5 of each of the second cappinglines 144XP.

Subsequently, the processes described above with reference to FIGS. 151and 15J may be performed.

Referring to FIG. 16E, the second mask pattern 420 including a pluralityof line patterns which extend in parallel along a second direction(e.g., the Y direction) may be formed on a second conductive layer 120P.

A process similar to the processes described above with reference toFIGS. 16A to 16D may be performed. A plurality of second gaps GY1A maybe formed by anisotropic-etching the stacked structure CPS, and anisotropic etching process of removing side portions of a plurality ofvariable resistance layers 132 and side portions of a plurality ofselection devices 134 may be performed. Thus, a plurality of bit lines120 may be formed.

Referring to FIG. 16F, a sixth preliminary capping layer 140L2 may beconformally formed on a top and a side wall of each of a plurality ofstacked lines CPL and may fill a third undercut area 132YU and a fourthundercut area 134YU.

Referring to FIG. 16G, etching back of the sixth preliminary cappinglayer 140L2 in the second gaps GY1A until a top of a bottom electrodelayer BEL is exposed may be performed. A plurality of first cappinglayers 142 may be formed on side walls of the variable resistance layers132, and a plurality of second capping layers 144 may be formed on sidewalls of the selection devices 134.

Subsequently, the processes described above with reference to FIG. 15Omay be performed.

In the method of manufacturing the memory device 100 according to anexemplary embodiment of the present inventive concept, a number of timesan etching process and a process of forming the capping layers 142 and144 are performed may be reduced, and thus, the memory device 100including the capping layers 142 and 144 may be manufactured by asimpler process.

FIGS. 17A to 17D are cross-sectional views illustrating a method ofmanufacturing a memory device according to an exemplary embodiment ofthe present inventive concept. Referring to FIGS. 17A to 17D, likereference numerals may refer to like components described with referenceto FIGS. 1 to 16G and thus duplicative descriptions may be omitted.

First, the process described above with reference to FIGS. 15A to 15Cmay be performed.

Referring to FIG. 17A, the insulation liner 146 may be conformallyformed on an inner wall of each of a plurality of first gaps GX1B. Theinsulation liner 146 may be conformally formed on a bottom of each of aplurality of top electrode lines TEL and a side wall of each of aplurality of variable resistance layer lines 132L in a first undercutarea 132XU. The insulation liner 146 may include silicon oxynitride orsilicon nitride and may be formed to have a thickness of from about 2 nmto about 50 nm through a CVD process, an ALD process, or a PECVDprocess.

Referring to FIG. 17B, a top of the preliminary bottom electrode layerPBE may be exposed by performing the anisotropic etching process and theisotropic etching process described above with reference to FIG. 15F.

According to an exemplary embodiment of the present inventive concept,in the etching process, a portion of the insulation liner 146 which isdisposed on a top of a first mask pattern 410 and a top of thepreliminary middle electrode layer PME may be removed, and a portion ofthe insulation liner 146 which is disposed on a side wall of each of thetop electrode lines TEL and in the first undercut area 132XU may remain.However, exemplary embodiments of the present inventive concept are notlimited thereto.

A seventh preliminary capping layer 140L3 may be conformally formed onthe inner wall of each of the first gaps GX1B.

Referring to FIG. 17C, by etching back the seventh preliminary cappinglayer 140L3 in each of the first gaps GX1B until the top of thepreliminary bottom electrode layer PBE is again exposed, a plurality offirst capping lines 142XP may be formed on side walls of the variableresistance layer lines 132L, and a plurality of second capping lines144XP may be formed on side walls of a plurality of selection devicelayer lines 134L.

Referring to FIG. 17D, the second mask pattern 420 including a pluralityof line patterns which extend along a second direction (e.g., the Ydirection) may be formed on the stacked structure CPS. Subsequently, theplurality of second gaps GY1A may be formed by anisotropically etchingthe stacked structure CPS with the second mask pattern 420 as an etchmask.

The insulation liner 146 may be formed by performing processes similarto the processes described above with reference to FIGS. 17A to 17C, anda process similar to the processes described above with reference toFIGS. 16A to 16D may be performed. Thus, the memory device 100 c may bemanufactured.

While the present inventive concept has been particularly shown anddescribed with reference to exemplary embodiments thereof, it will beunderstood that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present inventiveconcept.

What is claimed is:
 1. A memory device, comprising: a substrate; aninsulating interlayer disposed on the substrate; a word line disposed onthe insulation interlayer; a bottom electrode disposed on the word line;a selection device disposed on the bottom electrode, wherein a firstcapping layer is disposed on a side wall of the selection device; amiddle electrode disposed on the selection device; a variable resistancelayer disposed on the middle electrode, wherein a second capping layeris disposed on a side wall of the variable resistance layer; a topelectrode disposed on the variable resistance layer; and a bit linedisposed on the top electrode.
 2. The memory device of claim 1, whereinthe first capping layer has a first thickness in a first directionsubstantially parallel to a top surface of the substrate, the secondcapping layer has a second thickness in the first direction, and thesecond thickness is substantially greater than the first thickness. 3.The memory device of claim 1, wherein the selection device has a firstwidth in a first direction substantially parallel to a top surface ofthe substrate, the variable resistance layer has a second width in thefirst direction, and the second width is substantially smaller than thefirst width.
 4. The memory device of claim 3, wherein the word line hasa third width in the first direction, wherein the third width issubstantially greater than the first width or the second width.
 5. Thememory device of claim 1, further comprising an insulation patterndisposed on side walls of each of the first capping layer, the middleelectrode, and the second capping layer, wherein the insulation patternis separated from the side wall of the selection device by the firstcapping layer, and wherein the insulation pattern is separated from theside wall of the variable resistance layer by the second capping layer.6. The memory device of claim 1, further comprising an insulation linerbetween the second capping layer and the variable resistance layer. 7.The memory device of claim 1, wherein a side wall of the word line issubstantially aligned with a side wall of the first capping layer.
 8. Amemory device, comprising: a substrate; an insulating interlayerdisposed on the substrate; a word line disposed on the insulationinterlayer; a bottom electrode disposed on the word line; a selectiondevice disposed on the bottom electrode, wherein a first capping layeris disposed on a side wall of the selection device; a middle electrodedisposed on the selection device; a variable resistance layer disposedon the middle electrode, wherein a second capping layer is disposed on aside wall of the variable resistance layer; a top electrode disposed onthe variable resistance layer; and a bit line disposed on the topelectrode, wherein the selection device has a first width in a firstdirection parallel to a top surface of the substrate, the first width issubstantially smaller than a width of the word line or a width of thebit line, or wherein the variable resistance layer has a second width inthe first direction, the second width is substantially smaller than thewidth of the word line or the width of the bit line.
 9. The memorydevice of claim 8, wherein the second width is substantially smallerthan the first width.
 10. The memory device of claim 8, wherein thefirst capping layer has a first thickness in the first direction, thesecond capping layer has a second thickness in the first direction, andthe second thickness is substantially greater than the first thickness.11. The memory device of claim 8, further comprising an insulationpattern disposed on side walls of each of the first capping layer, themiddle electrode, and the second capping layer, wherein the insulationpattern is separated from the side wall of the selection device by thefirst capping layer, and wherein the insulation pattern is separatedfrom the side wall of the variable resistance layer by the secondcapping layer.
 12. The memory device of claim 8, further comprising aninsulation liner between the second capping layer and the variableresistance layer.
 13. The memory device of claim 8, wherein a side wallof the word line is substantially aligned with a side wall of the firstcapping layer.
 14. A memory device, comprising: a substrate; aninsulating interlayer disposed on the substrate; a word line disposed onthe insulation interlayer; a bottom electrode disposed on the word line;a selection device disposed on the bottom electrode, wherein a firstcapping layer is disposed on a side wall of the selection device; amiddle electrode disposed on the selection device; a variable resistancelayer disposed on the middle electrode, wherein a second capping layeris disposed on a side wall of the variable resistance layer; a topelectrode disposed on the variable resistance layer; and a bit linedisposed on the top electrode, wherein the first capping layer has afirst thickness in a first direction substantially parallel to a topsurface of the substrate, the second capping layer has a secondthickness in the first direction, and the second thickness is differentfrom the first thickness.
 15. The memory device of claim 14, wherein thesecond thickness is substantially greater than the first thickness. 16.The memory device of claim 14, wherein the selection device has a firstwidth in the first direction, the variable resistance layer has a secondwidth in the first direction, and the second width is substantiallysmaller than the first width.
 17. The memory device of claim 16, whereinthe word line has a third width in the first direction, and the thirdwidth is substantially greater than the first width or the second width.18. The memory device of claim 14, wherein a side wall of the word lineis substantially aligned with a side wall of the first capping layer.